1. Field of the Invention
The present invention relates to a video distribution system reducing video data traffic and a video distribution method therefor, which are applicable to such as a cache control server and a video distribution server for executing video distribution over a communication network.
2. Description of the Background Art
Use of video distribution services for distributing video data over a communication network has been expanded in recent years. Video traffic of video distribution is claimed to make up a large share of network traffic. In addition, the video traffic is known for conveying a lot of redundant video data.
Diminishment of such redundant video data traffic reduces a load on the video traffic, leading to increase in efficiency of the traffic over the network.
A non-patent document, Shogo ANDO, et al., “A Study of In-Network Cache for Redundancy Elimination at Network Edges”, The Institute of Electronics, Information and Communication Engineers (IEICE), Technical Report of IEICE, 2011, presents a known art for diminishing the traffic of redundant video data, which is called as In-Network cache technique, in which a given pair of routers having a cache function caches packets flowing between the routers, so that one of the routers does not transfer between the routers cached packets and redundant packets so as to permit the destination router to send packets out from a cache. It can reduce redundant packets between routers and consequently diminish video traffic.
However, the properties of the video distribution cause a tendency in the data volume of a single content to be larger than that of average data, and thus further diminishment is needed to the video traffic because use of video distribution services will be expanded more and more in the future.
In addition, when the user watches or listens to contents, it is preferable to allow the user to watch or listen at a transfer rate defined by a content distribution server. However, the diminishment of the video traffic conducted simply by applying the technique taught in the aforementioned Shogo ANDO, et al., cannot implement stable video data transfer, and thereby delays may be caused during watching the video. Hence, it is necessary to transfer video data such that the transfer rate will be smoothed and to distribute contents at a transfer rate close to that defined by the content distribution server.